Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
HARDCASTLE
As described in historical dictionaries
Patronymica Britannica (1860)
HARDCASTLE. Must be, I think, a contraction of Harden Castle, the ancient residence of the Scotts of Harden, and a line specimen to this day of a border fortress, in Roxburghshire.
Origin: English
Region of origin: British Isles
Country of origin: England
Religion of origin: Christian
Language of origin: English